We have previously obtained data from frogs which suggested that one of the mechanisms basic to olfactory discrimination may be a chromatographic- like process across the mucosa. That is, electrophysiological and chromatographic studies have given strong but indirect evidence that the molecules of different odorants are distributed over the olfactory mucosa in different patterns. We will pursue this line of investigation in frogs and other species by defining exactly how the molecules are distributed to the receptors, what parameters affect these distributions, and how these distributions may make an impact upon the processing of olfactory information by the olfactory central nervous system. We will proceed as follows: (1) By presenting animals with tritium-labelled odorants and by measuring the resultant radioactivty in different mucosal regions with a liquid scintillation counter, we will map exactly how the molecules of different odorants are distributed across the length and breadth of the olfactory receptor sheet. The stability of these distribution patterns will be tested as a function of stimulus duration, concentration and flow rate. (2) Using autoradiographs of horizontal mucosal sections, we will follow the distribution of the molecules vertically through the depth of the mucosa, noting particularly any differential filtering of different chemicals by either the mucus or the olfactory cilia. (3) Autoradiographic techniques and liquid scintillation counting will be used to determine the pathways by which odorant molecules are removed from the olfactory mucosa. (4) By recording from single mitral cells in the olfactory bulb previously shown by electrical stimulation to receive their input from particular regions of the olfactory receptor sheet, we will determine whether the differential molecular distributions established across the mucosa by the chromatographic effect are topographically represented by a group of mitral cell in the olfactory bulb. (5) Using chemicals whose regional chromatographic effect is known and by recording from single mitral cells whose regional input is selectively blocked, we will determine whether particular regions of the olfactory mucosa are mutually inhibitory, facilitatory, or without effect.